Agreed 100%. User-agent discrimination should be illegal. People always use the "security" excuse against it, but if changing your UA header is enough to get past the checks, it's clearly in the realm of security theater.

It will make adoption of free software even harder.

Depends what you mean by "free software", but I assume you're referring to independent/competing implementations and not "software developed corporate interests, who have only decided to make the source public" (like Big Browser.) Chrom[e/ium], and browsers based on it, are "free" after all.

That said, remote attestation is the real enemy of your freedom and privacy.